A hook member made by bending a rod member is often welded to a seat frame consisting of a pipe member for the purpose of attaching the seat to a vehicle body.
Such a hook member is made by bending an intermediate part of a rod-like member into the shape of letter U, and forming an engagement portion for a seat frame by joining its two ends. Typically, an engagement portion is shaped so as to be able to partially wrap around a pipe member in order to ensure a sufficient welding length in welding it to the seat frame.
However, it has been difficult to mechanize and automate the process of positioning the hook member relative to the seat frame because of the interference between the seat frame pipe and the engagement portion. Also, the hook member is so curved and complicated in shape that it cannot stay stable when it is placed unsupported and it is therefore difficult to clamp it to an assembly jig or the like. Consequently, a significant part of the work related to the assembling of the hook member to the seat frame had to be done manually, and it has been difficult to improve manufacturing precision and production efficiency.